λ hfmt --help
hfmt - format Haskell programs
Usage: hfmt [-d|--print-diffs] [FILE]
  Reformats Haskell source files by applying HLint, hindent, and
  stylish-haskell.
Available options:
  -h,--help                Show this help text
  -d,--print-diffs         If a file's formatting is different, print a diff.
  -s,--print-sources       If a file's formatting is different, print its
                          source.
  -l,--print-paths         If a file's formatting is different, print its path.
  -w,--write-sources       If a file's formatting is different, overwrite it.
  FILE                     Explicit paths to process.
                            - A single '-' will process standard input.
                            - Files will be processed directly.
                            - Directories will be recursively searched for source files to process.
                            - .cabal files will be parsed and all specified source directories and files processed.
                            - If no paths are given, the current directory will be searched for .cabal files to process, if none are found the current directory will be recursively searched for source files to process.
Exit Codes:
  0 = No error
  1 = Encountered I/O or other operational error
  2 = Failed to parse a source code file
  3 = Source code was parsed but cannot be formatted properly
  4 = Formatted code differs from existing source (--print-diffs only)